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Omega-3 Fats and Cognitive Health
By Carrie Dennett, MPH, RDN, CD
As clients and patients age, concerns about developing chronic health conditions such as type 2 diabetes, heart disease, and cancer increase. But so does the desire to remain mentally sharp. Interest in preventing or delaying Alzheimer’s disease, dementia, and other forms of cognitive decline is strong, giving rise to several brain health claims associated with certain foods, nutrients, and supplements.
For example, many older adults take omega-3 fatty acids in supplement form to help prevent age-related cognitive decline. But does the research match the hype? It’s well documented that omega-3s—especially DHA and EPA, the types found in fish and seafood—are critical for prenatal and early childhood brain development, in part because the brain contains a high level of omega-3s. But what might this mean for adult brains?
Much of the focus on omega-3s and adult health has centered on heart health, and what’s good for the heart may be good for the brain—after all, stroke is one type of CVD. But research on omega-3s and cognitive health is less robust. A 2020 study that drew data from the 2011–2014 National Health and Nutrition Examination Survey found that omega-3 intake might be inversely associated with low cognitive performance in adults older than age 60. The authors say this is biologically plausible, but the findings must be confirmed by long-term prospective studies.1
A 2020 World Health Organization–funded systematic review and meta-analysis examined 38 randomized controlled trials that compared higher vs lower intake of omega-3 fatty acids from supplements or foods, as well as studies that simply advised the intervention group to alter their intake. The included studies were published between 1978 and 2018, with an average duration of 21 months. The shortest trials included were 24 weeks in length, because other research suggests this is the minimum duration of supplementation needed to balance levels of omega-3s in the brain.2
Most of the trials used omega-3 supplements. One advised participants to eat more oily fish, two provided fish sausages, and one provided omega-3 enriched margarine. Doses ranged from 150 mg/day to 4.4 g/day, but most were in the range of 400 to 2,400 mg/day. Participants included people with normal and impaired cognition at baseline.2
The results suggest that omega-3s have little or no effect on preventing new neurocognitive illness or impairment. There was a statistically significant but clinically unimportant effect on global (overall) cognition, and the authors noted that because the three trials that provided most of the participant data were at least three years long—with the largest being six years in duration—it’s unlikely that the small effect size was because the trials were too small or too short.2
The authors concluded that health care providers should advise people who are concerned about cognitive health that taking omega-3 supplements is neither helpful nor harmful. They also stressed the need for well-designed, long-duration studies assessing the impact of increasing intake of oily fish as well as nuts and other foods high in the plant-based omega-3 alpha linolenic acid (ALA).2
Studies on Fish Intake
It’s well known that Americans don’t eat the recommended amount of fish and seafood, including the types of fatty fish—such as salmon and sardines—that are high in omega-3s. What might this mean for the brain? A 2018 Finnish study of 2,612 middle- and older-age adults (aged 43 to 70 at baseline) looked at fat intake and cognitive decline, assessing cognitive function at baseline and at five-year follow up. The authors found no consistent association between fatty fish consumption and cognitive decline, but did find that higher omega-3 intake—especially ALA intake—was associated with a slower decline in global, or overall, cognitive function. Higher intake of DHA and EPA appeared to prevent only cognitive decline in subjects with a specific APOE (apolipoprotein E) genotype—carrying two copies of the APOE e4 allele.3 APOE is a protein that combines with fats in the blood to form lipoproteins, and carrying one or two copies of the e4 allele has been linked to an increased risk of developing late-onset Alzheimer’s disease along with an earlier onset of memory loss than is observed in Alzheimer’s patients who don’t have this genotype.3,4 Carrying the e4 allele also has been implicated in CVD.4
A 2016 Rush University study found a similar connection. Among participants in the Rush Memory and Aging Project, eating fish once per week was associated with slower rates of decline in semantic memory (the ability to remember facts) and perceptual speed (the ability to quickly process new information, which is important when, say, driving). However, only APOE e4 carriers with weekly fish consumption showed slower rates of decline in global cognition—as well as episodic memory, semantic memory, and perceptual speed—with weekly seafood consumption. These assessments were made over an average 4.9 years of follow-up.5
Bottom Line
There are clear benefits to eating the recommended amount of fish and seafood, even if the scientific jury is still out on the impacts on cognitive health in adults. Fish and seafood are healthful sources of protein and have benefits for heart health. Dietitians can advise patients to increase intake—which may require offering instructions or resources for becoming more comfortable preparing seafood. As for omega-3 supplements, for now this may be a matter of personal choice, with the understanding that they may not offer the desired benefits.
— Carrie Dennett, MPH, RDN, CD, is the nutrition columnist for The Seattle Times, owner of Nutrition By Carrie, and author of Healthy for Your Life: A Holistic Guide to Optimal Wellness.
References
1. Dong X, Li S, Chen J, Li Y, Wu Y, Zhang D. Association of dietary ω-3 and ω-6 fatty acids intake with cognitive performance in older adults: National Health and nutrition examination Survey (NHANES) 2011-2014. Nutr J. 2020;19(1):25.
2. Brainard JS, Jimoh OF, Deane KHO, et al. Omega-3, omega-6, and polyunsaturated fat for cognition: systematic review and meta-analysis of randomized trials [published online April 15, 2020]. J Am Med Dir Assoc. doi: 10.1016/j.jamda.2020.02.022.
3. Nooyens ACJ, van Gelder BM, Bueno-de-Mesquita HB, van Boxtel MPJ, Verschuren WMM. Fish consumption, intake of fats and cognitive decline at middle and older age: the Doetinchem Cohort Study. Eur J Nutr. 2018;57(4):1667‐1675.
4. APOE gene. Genetics Home Reference website. https://ghr.nlm.nih.gov/gene/APOE#. Updated June 9, 2020.
5. van de Rest O, Wang Y, Barnes LL, Tangney C, Bennett DA, Morris MC. APOE ε4 and the associations of seafood and long-chain omega-3 fatty acids with cognitive decline. Neurology. 2016;86(22):2063‐2070.